PC speaker?

[Fabrizio Gennari]

My PC case came without a speaker (the small one, connected directly to
the motherboard, that just beeps at startup, and used to play sounds in
old DOS games).

I wonder what type of speaker is needed. I heard of piezo transducers,
buzzers and sounders, but I'm not sure about the difference between them.
What I think is that I don't need something that beeps when connected to a
DC source, but something like a small loudspeaker, that reproduces the
input waveform as a sound.

So: what type of part is needed as speaker? How many Ohms? And how are the
motherboard connectors called? The ones that connect on the wires on one
side, and plug to the pins on the motherboard. On Farnell I found Molex
10-11-2023 and 10-11-2043, that look like they are the right ones, but I
don't know for sure.

Regards,
Fabrizio

 

[Andy]

Any speaker will suffice. The circuit that drives the speaker is very
primitive. One side of the speaker goes to +5 volts. The other side is
connected through a current limiting resister to a transistor that
switches to ground.

 

[Paul]

Any speaker will suffice. The circuit that drives the speaker is very
primitive. One side of the speaker goes to +5 volts. The other side is
connected through a current limiting resister to a transistor that
switches to ground.

My current computer case employs a 8 ohm 0.25 watt speaker.

An example of a speaker drive circuit can be seen on PDF page 32 here.

http://www.intel.com/design/chipsets/designex/BXDPDG10.PDF

If I connected my 8 ohm speaker to that circuit, the power
it would receive might be around the 1/8th watt level.

One of the defects of that circuit, is that the speaker is
connected directly to +5V. I've heard of one case, where
someone managed to pinch the red speaker wire to the chassis
metal, and the resulting short circuit to ground caused the wire
to melt and the plastic to burn.

*******

The other kind of speaker type is piezoelectric.

http://www.clearpc.ca/catalog/images/speaker.JPG

Examples of the various types are here. The frequency
response of these is not that flat.

http://www.murata.com/catalog/p37e.pdf

Paul